JPH0431195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to the structure of a semiconductor laser array device.

<Conventional technology> When operating a semiconductor laser at high output, considering the practicality of using a single semiconductor laser, the output
The limit is about 80mW. Therefore, research is actively being conducted on semiconductor laser array devices in which a plurality of semiconductor lasers are arranged in parallel on the same substrate to increase output.

By the way, as shown in FIG. 7, a plurality of semiconductor lasers 1 are arranged in parallel with optical coupling,
When a uniform gain is given to each semiconductor laser 1, the phase of each laser beam is more synchronized at 0° phase (0° phase mode) as shown at 2 in Fig. 7 than at 3 in Fig. 7. As shown, oscillation is likely to occur when the phase of each laser beam is reversed by 180° (180° phase mode). This is because the electric field distribution of light matches the gain distribution better in the 180° phase mode than in the 0° phase mode, resulting in a higher oscillation gain.

On the other hand, the far-field pattern of the laser beam emitted from the semiconductor laser array device is as shown in Figure 6a in the 0° phase mode.
It is a single peak as shown in Figure 6b, and can be focused on a single spot with a lens.In the 180° phase mode, it becomes a multimodal peak as shown in Figure 6b, and can be focused on a single spot with a lens. It cannot be focused on a single spot, making it unsuitable as a light source for optical disks, etc. Therefore, it is desired that the phases of the output lights from each semiconductor laser of the semiconductor laser array device be 0° phase synchronized.

<Objective of the Invention> Therefore, the present invention has a simple structure in which the output lights of a plurality of optically coupled semiconductor lasers arranged in parallel are synchronized at 0 degrees, and a radiation pattern with a single peak is achieved. An object of the present invention is to provide a semiconductor laser array device that emits laser light.

<Structure and Principle of the Invention> In order to achieve the above object, the present invention is characterized in that a semiconductor laser array device has a waveguide structure that converts laser light guided in a 180° phase mode into a 0° phase mode. There is. FIG. 1 shows an example of a waveguide structure of a semiconductor laser array device of the present invention viewed from above. Each waveguide W, W, . . . is arranged in parallel and optically coupled, and is composed of three regions 10, 11, 12 in the direction of the waveguides W, W, . In regions 10 and 12, symmetrical waveguide parts W ₁₀ and W ₁₂ are lined up, whereas in region 11
In this case, asymmetrical waveguide portions W ₁₁ -a and W ₁₁ -b are periodically arranged in a direction perpendicular to the waveguide direction. Therefore, the waveguide portion W ₁₁ −a and the waveguide portion
W ₁₁ -b has a different effective refractive index. The effective refractive index difference ΔN between the waveguide portions W ₁₁ -a and W ₁₁ -b is set so as to satisfy the following equation.

2π/λ ₀ ΔN・l ₂ = mπ (m is an odd number) ...(1) Here, l ₂ is the length of the waveguide portions W ₁₁ -a, W ₁₁ -b, and λ ₀ is the wavelength of light in vacuum. It is.

In this way, the guided light propagating through the symmetrical parallel waveguide portions W ₁₀ , W ₁₀ , ..., W ₁₂ , W ₁₂ , ... in the regions 10 and 12 is transmitted through the asymmetrical waveguide portion W ₁₁ -a in the region 11. , W ₁₁ -b, the guided light passing through the waveguide section W ₁₁ -a and the waveguide section
The phase difference of the guided light passing through W ₁₁ -b changes by 180°. Therefore, when the 180° phase mode light whose phase is alternately reversed by 180° in each waveguide passes through the waveguide portions W ₁₁ -a and W ₁₁ -b of region 11, the phases are synchronized in each waveguide. Conversely, when light in the 0° phase mode passes through the region 11, it is converted to the 180° phase mode.

Now, assuming that uniform gain is given to each waveguide W, W, the waveguide portions W ₁₀ , W ₁₂ in regions 10 and 12
So the 180° phase mode provides more gain than the 0° phase mode. Therefore, in regions 10 and 12, 180° phase mode light propagates more easily. Area 10,
If the lengths of the waveguide portions W ₁₀ and W ₁₂ of 12 are l ₁ and l ₃ and l ₁ < l ₃ , the light 15 in the 180° phase mode propagates in the region 12, and as described above, the light 15 in the 180° phase mode propagates in the region By passing through 11, the 0° phase mode light 16
The light in that state propagates in the region 10, and output light with a 0° phase synchronization is obtained from the output end face 17 of the region 10. At this time, conversely, in area 12
It does not occur that the 0° phase mode propagates, is converted to the 180° phase mode in region 11, and the 180° phase mode propagates in region 10. This is because the threshold gain required for oscillation is lower in the above-mentioned state than in this state. Similarly, when l ₁ >l ₃ , phase-synchronized output light is obtained from the output end face 18 of the region 12. However, when l ₁ = l ₃ ,
This is not desirable because the 0° phase mode and the 180° phase mode coexist in oscillation in regions 10 and 12.

As mentioned above, in this semiconductor laser array device, the laser light guided in the 180° phase mode is converted into the 0° phase mode internally, and from the emission end face, the laser beam is 0° phase synchronized and unimodal. Output light with a pattern can be obtained.

<Example> Hereinafter, the present invention will be applied to a semiconductor laser using VSIS (V-
We will discuss the case where a channeled substrate inner stripe type semiconductor laser is applied.

FIG. 2 shows a diagram of the semiconductor laser array device of the present invention viewed from the resonator end face. p-GaAs substrate 20
An n-GaAs current blocking layer 21 is grown thereon by a crystal growth method such as liquid phase epitaxial (LPE) method. Next, by photolithography and etching techniques, a plurality of parallel V-shaped grooves 22 having the same shape as shown in FIG. 1 are formed from the current blocking layer 21 to a depth reaching into the substrate 20.
In order to provide regions 11 in which the effective refractive index of the waveguide shown in FIG. A window is opened in a portion corresponding to the waveguide portion W ₁₁ -b in FIG. 1, and etching is performed again. Then, a groove 32 is formed as shown in FIG. 3, and the depth of this groove 32 is deeper than the depth of the adjacent groove 22. That is, the grooves 32 and 22 become deeper alternately in the direction perpendicular to the waveguide. In this way, only the groove 22 is formed in the portions corresponding to the regions 10 and 12 on both sides of the region 11, and
In the portion corresponding to region 11, p-Al x Ga 1 -xAs cladding layers 23, 33, p-Al _x Ga ₁ -xAs cladding layers 23, 33, p-Al or n-AlyGa ₁ -yAs active layer 24, 34, n-AlxGa ₁ -xAs cladding layer 2
5, 35 will grow sequentially. However, x>y. Furthermore, n ⁺ -GaAs cap layers 26 and 36 are grown. At this time, as shown in FIG. 2, a flat active layer is obtained in regions 10 and 12, whereas in region 11, the shape of the active layer 34 grown thereon is determined by the depth of grooves 22 and 32. A flat active layer 34a is obtained on the shallow groove 22, and a curved active layer 34b is obtained on the deep groove 32. In FIG. 3, adjacent waveguide portions W ₁₁ -a, W ₁₁ -b
Letting the effective refractive index difference of ΔN be, the length l ₂ of the region 11 is set so as to satisfy the above-mentioned formula (1). After that, p-type resistive electrodes 27, 37 are placed on the substrate side, and n-type resistive electrodes 28, 3 are placed on the growth layer side.
8 was formed, a mirror was formed by the cleavage method so that the cavity length was 200 to 300 μm, and the mirror was mounted on a copper block to fabricate a semiconductor laser array device.

Next, a second example will be described. First, as shown in FIG. 4, n-
A GaAs current blocking layer 21 is grown. When viewed from above on the surface, as shown in FIG.
A plurality of symmetrical V-shaped grooves 22-40, 22-42 arranged in parallel at 0, 42, and a plurality of V-shaped grooves 22-41a, 22-41b whose groove width periodically changes alternately in the central region 41. A cladding layer 23, an active layer 24, a cladding layer 25, a cap layer 26, etc. are sequentially grown thereon again by the LPE method. Wide groove 22-41 in region 41
A wide waveguide and a narrow waveguide are formed on the narrow width 22-41b, respectively, and the effective refractive index difference between the wide waveguide and the narrow waveguide is ΔN Then, the length l ₁ of the region 41 is set to satisfy equation (1). The following steps are the same as in the first embodiment described above.

When the semiconductor laser array devices of the first and second embodiments are manufactured with appropriate structural parameters that satisfy the above-mentioned formula 1, the characteristic is that the oscillation threshold is 150 mA.
Then, the light emitted from the end face 17 near the regions 11 and 41 that causes a 180° phase difference change in the adjacent waveguide portions oscillates in a single transverse mode up to an output of 100 mW.
As shown in Figure 6a, the far-field image has a sharp unimodal peak (half width 4°), and the emitted laser beam
It was found that they were 0° phase synchronized. Furthermore, the light emitted from the end surface 18 opposite to the end surface 17 is output.
It oscillates in a single transverse mode up to 100 mW, and its far-field pattern has multimodal peaks (9° apart) as shown in Figure 6b, indicating that the emitted laser beam has a 180° phase inversion. I understand.

In this way, it has been found that in a semiconductor laser array device, if a waveguide section is provided in which the phase difference of light propagating through adjacent waveguides changes by 180 degrees, output light that is phase-synchronized by 0 degrees can be obtained. Ivy.

Note that although the above embodiments have been described with reference to GaAs-GaAlAs-based materials, the present invention is not limited thereto, and can be applied to InP-InGaAsP-based materials and other various materials. In addition, the striped structure
In addition to the VSIS structure, it is also possible to use other internal stripe structures or other element structures.

<Effects of the Invention> As described above, according to the present invention, multiple laser beams are oscillated in phase synchronization, and high-power laser beams can be emitted with a radiation pattern having a sharp single peak. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing the waveguide of the semiconductor laser array device of the present invention from above and explaining its operating principle. FIG. 2 is a resonator end view of the semiconductor laser array device according to the first embodiment of the present invention. FIG. 3 is a sectional view of a portion of the above embodiment in which the 180° phase difference is changed. FIG. 4 is an end view of a resonator according to a second embodiment of the present invention. FIG. 5 is a top view of a waveguide structure in a second embodiment of the present invention. FIGS. 6a and 6b are diagrams showing far-field images in the horizontal direction of the semiconductor laser array device of the present invention. 7th
The figure shows a plurality of optically coupled parallel waveguides and the shapes of modes propagating through them. W...Waveguide, W ₁₀ , W ₁₁ -a, W ₁₁ -b,
W ₁₂ ...Waveguide part.

Claims (1)

[Claims] 1. In a semiconductor laser array device including a plurality of optically coupled parallel waveguides, a plurality of waveguide portions having the same effective refractive index in a direction perpendicular to the direction of the waveguides. a first region in which light propagates through the plurality of waveguide sections in a 180° phase mode in which the phases of the light alternately differ by 180°; It has a plurality of waveguide sections in which the refractive index alternately changes,
The difference in the refractive index △N is (2π/λ ₀ )△N・l ₂ = mπ (m is a parsitial number, l ₂ is the length of the waveguide section, and λ ₀ is the wavelength of the light in vacuum)
and a second region that satisfies the following relationship and changes the phase of the 180° phase mode light from the first region by 180° to convert it into 0° phase mode light and output it from the output end face. Semiconductor laser array equipment. 2. In the semiconductor laser array device according to claim 1, the active layer constituting the waveguide portion of the second region is composed of a flat active layer and a curved active layer in a direction perpendicular to the waveguide direction. A semiconductor laser array device in which the effective refractive index of the waveguide portion is changed in a direction perpendicular to the waveguide direction by arranging layers alternately. 3. In the semiconductor laser array device according to claim 1, the width of the waveguide portion in the second region is alternately changed in a direction perpendicular to the waveguide direction. A semiconductor laser array device in which the effective refractive index of the waveguide portion is changed in the direction.